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I wouldn't break up with someone just because I found someone else attractive. If I were to break up with someone, there would have to be other problems that can't be fixed for me to do so.

What that guy did was pretty bad. If he really wanted to be with someone else, then he should have broke up with the first girl way before the second girl broke up with her boyfriend. Keeping the first girl as backup in case the second girl never left her boyfriend is messed up.

If you'd rather be in a relationship with someone else, then save the person you're with time and effort if you're not into it anymore. Don't lead them on so you don't have to be alone. You do your time alone if you want something else so badly.

I don't mind not being someone's first choice. It's not out of the ordinary for people to fall out of love with one another. You can feel very much in love in the moment but it doesn't mean it'll always last. Though what his guy is different, as he lead the first girl on and didn't just break up with her. That's when things get messy. Not being in love anymore is different than just using someone because you yourself don't want to be alone.

Being with someone who is clingy and desperate is pretty unhealthy. If they want to take up too much of your time then that's not fair. You can't spend that much time with someone and expect things to still be good and healthy. He just thinks you're crazy because you didn't want him, that's all it is.